1. Field of the Invention
The present invention relates to an image processing apparatus which is suitable for use in, for example, a facsimile apparatus, an electronic filing apparatus, an image reader, a digital copier, or the like.
2. Description of the Prior Art
According to a conventional method of binarized gradation processing an image by way of a dither method, the image signal read out is directly compared as an analog signal with the dither threshold value or after it has been converted to a digital signal, this digital signal is compared with the dither threshold value and, in this case, the dither threshold value is two-dimensionally changed in correspondence to the division of the read image.
FIG. 1 is a diagram showing a concept of binarization by way of a dither method. The image signal is compared with the dither threshold value stored in a memory 101 such as a ROM or the like by a comparator 100. For example, a white signal is outputted when the image signal is higher than the dither threshold value, while a black signal is outputted in the opposite case. The values shown in the memory 101 represent the dither threshold values.
By use of this method, the image of a photograph or the image of continuous gradations of a half-tone can be reproduced as a beautiful gradation image. On the contrary, however, there is a drawback
that the resolution deteriorates, since pattern images such as characters, diagrams, or the like are also subjected to gradation processing.